DEDHAM – Almost 20 years after a young Milton man was shot to death on a side street in Upper Mills, Kenyatte E. Murrell and Jameel A. Williams have pleaded guilty to manslaughter.

Murrell, 41, and Williams, 37, were originally convicted in 2003 in the murder of Milton High School graduate Gregory Cormier, but that conviction was overturned five years later by the State Supreme Judicial Court with a reprimand for prosecutorial misconduct.

Murrell and Williams have been held in state prison in Norfolk, awaiting a new trial on first-degree murder charges, since that ruling.

On Tuesday in Norfolk Superior Court, Judge Raymond J. Brassard sentenced Murrell to a 19 1/2 -year prison term and Williams to an 18-year prison term on the manslaughter charges.

Both men were also sentenced to concurrent prison terms of 15-20 years after each pleaded guilt to a charge of armed assault with intent to murder for shooting the passenger in Cormier’s car, Wayne Jackson.

Williams and Murrell were convicted in late 2003, partly from testimony by Shawn Castle, the prosecution’s key witness. Castle said he drove the two men to the murder site and then gave them a ride back to another gang member’s house.

Castle was later deported to his native country of Trinidad as a result of other convictions. After the supreme court overturned the conviction, Norfolk District Attorney Michael Morrissey sent a State Police lieutenant to Trinidad to search for Castle, who was eventually found but was unwilling to return to Massachusetts to testify.

Prosecutors also said that one police witness has died since the 2003 trial, and another is retired.

“This was a difficult case in 2003. The loss of multiple witnesses, including the driver, left us with the choice between accepting a plea to manslaughter and the very real potential of walking away with a not guilty verdict after another trial,” Morrissey said in a written statement. “We have to deal with the state of the evidence today and make our decisions on that basis.”

Cormier’s killing shocked Milton, which at the time hadn’t seen much of Boston’s street violence spill over into its neighborhoods.

Cormier was 20 and had played basketball for Milton High School. He was fatally shot in his Mazda as he and his friend Wayne Jackson drove through Upper Mills.

Chris Burrell may be reached at cburrell@ledger.com or follow on Twitter @Burrell_Ledger.